OREGON STATE UNIVERSITY Extension Service
SP 50-538 Reprinted March 2013
PRESERVING FOOD WITH HELP FROM YOUR MICROWAVE
The microwave can be a big time saver. Although it has many uses in food
preservation, there are also limitations. This sheet gives some tips for using the
microwave and also some no-no’s.
CANNING
The microwave cannot be used to safely can either acid or low acid foods. When
preserving by canning, we need a high constant temperature for a given period of
time to destroy microorganisms. The microwave does not provide either constant
temperature or high enough temperatures to safely preserve food.
1. All acid foods (fruits and tomatoes) must be processed in a boiling water
canner (212°F).
2. All low acid foods (vegetables, meats, fish, and poultry) must be processed in
a pressure canner (240°F).
The microwave can, however, be used in the preparation of food for canning such
as: cooking apples for making applesauce, heating syrups used in canning fruits,
and precooking fruits and vegetables when canning using the hot pack method.
Boiling low acid home-canned foods in a microwave as a safety precaution before
eating is not recommended. A full 10 minutes of boiling is still needed because of
the time-temperature relationship necessary to destroy botulinal toxin. This would
result in overcooking if the microwave is used. Use the range instead.
FREEZING
The microwave can successfully be used in preparation of foods for the freezer.
Small quantities of vegetables can be blanched for freezing with some success.
Also sauces prepared for the freezer (like tomato, chili, and spaghetti sauce) can
be thickened without any problem of scorching in the microwave.
BLANCHING VEGETABLES
The microwave can be used with limited success for blanching small quantities of
vegetables for the freezer. Because microwave heating is uneven, it is important
to stir or rotate the food and cook in a tightly covered container.
Timing is very important. Overcooking causes the vegetables to become mushy
and tough.
Too little cooking will not adequately destroy the enzymes. The temperature is also
important because the microwave must heat the vegetables evenly. Microwave ovens
have some unevenness in cooking pattern, but this can be overcome by stirring or
rearranging the vegetables halfway through the cooking time.
When blanching vegetables in the microwave, it is important to cook only small
batches at a time (not more than one pound). Blanching should be done in a
covered glass casserole or microwave freezer bags.
It is recommended that 1-2 tablespoons water be added to the vegetables before
cooking. Microwave (high) 3-4 minutes per pound, stirring halfway through
cooking. Let stand one minute after cooking and then put blanched vegetables
immediately into cold water to cool. Drain and pack in moisture vapor-proof freezer
bags. Freeze immediately.
Note: Cooking times may vary but are usually half the cooking time of the same
fresh vegetable. Blanch vegetables to a temperature of 180°F.
Tips on freezing foods for microwave cooking
Be sure to package your frozen foods so they can be thawed and cooked in the
microwave with little or no handling. Package in moisture vapor-resistant,
packaging sturdy enough to withstand microwave cooking. Package in flat, thin
packages keeping the thickness 1-2 inches. This type of packaging will allow you
to cook your vegetables in the microwave without thawing first.
Don’t overcook frozen vegetables. Allow 5-10 minutes carry-over time to equalize
the temperature and tenderize the vegetables. Overcooking toughens and dries
out the food. A 10 oz. package of frozen vegetables will be cooked in 7-8 minutes
on high.
Sauces like tomato, spaghetti, salsa and chili are great cooked in the microwave
because there is no worry about scorching. These products are cooked until the
desired thickness is reached.
Cooking tip: Cook sauces in a large tall casserole or 2 quart pitcher. Cover container
and cook on high power until mixture boils and then uncover and reduce power to
medium (50%). Continue cooking until sauce reaches desired thickness. If sauce
spatters as it thickens, cover with a paper towel. Be sure to cool all sauces thoroughly
before packaging for the freezer.
Freezer Tomato Sauce
8 cups of ripe unpeeled tomatoes (chopped into pieces)
2 Tbsp. sugar
2 Tbsp. chopped fresh parsley
1 bay leaf
1 tsp. dried leaf basil
1 tsp. salt
1 tsp. dried leaf oregano
¼ tsp. pepper
2 stalks celery, chopped
Combine all ingredients into a large casserole dish and microwave high power 25-35
minutes or until all the vegetables are tender. Run the mixture through a food mill or
colander. Return to the microwave and cook until the desired thickness (10-15
minutes). Freeze sauce in 1 cup serving portions.
Note: A 1-cup portion will thaw in 4-5 minutes on high power.
DRYING
Except for herbs and mushrooms, drying foods in the microwave is not
recommended. Other foods contain too much moisture and will cook and become
tough in the long drying process.
The microwave can be used for pretreatment of fruits and vegetables before
drying them in a dehydrator, oven, or the sun.
Tips on drying herbs and mushrooms
Use food-grade microwave paper towels when drying. (The dye used in the
decorator towels and the scraps of metal in recycled towels can cause hot spots
that could catch the towels on fire.) Place paper towel on meat rack to dry herbs.
This way moisture can escape easier.
Dry in small quantities (1-2 cups) at a time. Layer the herbs and mushroom slices in
a single layer. Too large a quantity will cause them to cook and not dry well.
Dry the herbs until they are almost dry and then let them finish drying at room
temperature. Let herbs completely cool before packaging.
Allow 3-6 minutes per cup on high power for 600 watt ovens, 2-4 minutes for 650-700
watt ovens. Stir the herbs every 30 seconds after the first minute until dry.
Herbs commonly dried in the microwave are parsley, celery leaves, thyme and sage.
When drying mushrooms, clean the mushrooms, slice and arrange in a single layer
on paper towel on meat rack. Microwave on high 6-10 minutes or until the slices
are semi-leathery. Air dry to cool before storing.
Reconstituting Dried Foods
The microwave is great for reconstituting dried fruits and vegetables. Combine 1
cup of fruit or vegetable with ½ cup water and microwave covered 2-4 minutes,
stirring once. Let fruit sit a few minutes or until desired plumpness is reached. Let
vegetables sit 30 minutes before cooking or adding to soups and stews.
JAMS AND JELLIES
The microwave can be helpful when making jams and jellies. When making large
quantities, you really don’t save any time. However, the product will not stick so
constant stirring is not necessary and the clean-up is simple.
Tips on Making Jams and Jellies
Pot holders should be used since sugar mixture gets very hot. Cover products
when heating to speed up the cooking and melt the sugar crystals clinging to the
side of the container during the first part of cooking. When removing cover, be
sure to lift the lid away from you so you won’t get burned from the steam.
Use high power when cooking. Pour jellies and jams into hot sterilized jars and
process in a boiling water bath.
Strawberry-Rhubarb Jam (freezer jam)
1½ cups strawberry puree (approx. 1½ pints whole berries)
2 cups sliced fresh rhubarb
½ cup water
1 package powdered fruit pectin (1¾ oz.)
5 cups sugar
Combine rhubarb and water and pectin in a large bowl and mix well.
Microwave on high power covered 5-6 minutes or until rhubarb is tender and
pectin is dissolved. Stir once or twice.
Stir in sugar and microwave uncovered 3-4 minutes or until mixture comes to a
boil. Stir once.
When mixture boils, add strawberries and mix well.
Wine Jelly
2½ cups red or rose wine
3¼ cups sugar
1 envelope liquid pectin
Combine wine and sugar in a large bowl and mix well.
Microwave mixture uncovered on high power 5-6 minutes or until boiling. Stir once or
twice to equalize temperature.
When hot, pour in liquid pectin and blend well.
Microwave 1-2 minutes longer or until mixture returns to boiling.
Pour into sterilized jars, leaving ¼ inch headspace. Adjust lids and process half-pint
jars for 5 minutes in a boiling water bath.
Makes about 5 glasses.
Microwave Apple-Butter
8 medium apples, quartered and cored
1 cup apple cider or juice
1 cup sugar
1 tsp. ground cinnamon
¼ tsp. ground cloves
In a 2 quart casserole combine the apples and cider. Cover and microwave 8-12
minutes on high power stirring every 3 minutes until apples are tender. Press the
cooked apples through a food mill or sieve to puree.
Return mixture to casserole dish and add sugar and spices.
Microwave uncovered 10-15 minutes on high power. Stir often until the mixture
thickens.
Pour cooked butter into hot sterilized jars, leaving ¼ inch headspace.
Process half-pint jars 5 minutes in a boiling water bath.
PICKLES AND RELISHES
The microwave can be used when making quick pickles and relishes. The time saved
is not great when large quantities are cooked but clean-up is easy because food
doesn’t stick. It is important to stir the pickles and relishes as they cool.
Microwaved quick pickles and relishes need to be processed in a boiling water bath
according to processing directions in PNW355 – Pickling Vegetables.
Year Round Fresh Tomato Relish
In 1½ quart casserole, stir together:
1 Tablespoon prepared mustard
1 Tablespoon brown sugar
2 teaspoons vinegar
½ teaspoon seasoned salt.
Place in microwave and cook on high power 1 minute. Add:
2 cups finely chopped tomato
½ cup finely chopped celery
½ cup finely chopped green pepper
¼ cup finely chopped green onion
Return to microwave and cook uncovered 2 minutes.
Stir well and refrigerate at least 1 hour before serving to blend flavors.
Store leftovers in refrigerator. Makes about 3 cups of relish.
Beet Pickles
1 (16 ounce can) sliced beets
¼ cup white vinegar
1 tsp. salt
½ tsp. cinnamon
¼ tsp. allspice
In a 4 cup glass measuring cup, drain off beet juice and add vinegar, salt and
spices.
Microwave liquids 3-5 minutes or until the mixture comes to a boil.
Stir once or twice during the cooking.
Add beets to the hot juice mixture. Store in a covered container in the
refrigerator and serve as needed. Serves 4.
Source: OSU Master Food Preserver Program
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